I have a telemetry device connected to the same LAN as Comfort, which it seems uses an ethernet to serial port interface from the same manufacturer as used in Comfort. When the telemetry device (TEK608 Broadband gateway) is connected, Comfort Server Manager becomes unusable due to a constantly flickering display that will not respond to keyboard input.

I suspect the issue is that Comfort Server Manager is identifying both devices in rapid succession.

Is there any solution to this other than separating them on different subnets?

CSM discovers the Eth03 using a UDP broadcast method. It would be interesting to see what a wireshark trace of your device looks like. Would you be able to capture a wireshark trace?
The only thing I can think of that your device might be doing is to continuously broadcast other data on the same port that CSM uses and this is probably what confuses it.

Yes CS Manager only sends the request at the start and when you refresh, It doesnt like another CS Manafer session at the same time

You can disconnect the telemetry device to assign the IP address to UCM/ETH93 by CS Manager and close CS Manager It should not cause any problem if CS Mnager is not running so I dont think it will be a problem

Thanks to all for your responses. I'm not always on site so disconnecting devices is a bit problematic. Ideally I want them to coexist so that I can access the system remotely if necessary. Unless there's another way, perhaps the best solution is to place the telemetry device on another subnet, although that's an option I'd prefer to avoid.

If the problem is with Comfort Server manager, you do not need to access it after you set the IP address and Port. Once that is done, you dont need to run CS Manager anymore unless you wish to change the IP address and port again or upgrade the firmware